1. Field of the Invention
The present invention relates to an electric torque converter used in an automatic transmission and mounted on a hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor (an electric motor generator) for vehicle propulsion.
2. Description of the Prior Art
In recent years, it is strongly desired to improve fuel economy of automotive vehicles, for the purpose of protecting global atmospheric and saving earth resources. In order to reduce fuel consumption, there have been proposed and developed various hybrid vehicles. Hybrid vehicles in which an internal combustion engine and an electric motor (an electric motor/generator), both serving as a propelling power source, are arranged in series to each other or in parallel with each other, and operate at various running modes, such as a motorpropelled vehicle driving mode, an engine-propelled vehicle driving mode, a regenerative mode, a power-assist mode, an electric power generation mode, and the like. For example, during the power-assist mode, the engine (a primary power source) is assisted by the electric motor (a secondary power source). Also, when the hybrid vehicle is decelerating, the hybrid system operates at the regenerative mode during which the electric motor is employed to convert kinetic energy of the vehicle into electric energy and to regenerate electricity which is stored in a car battery. One such parallel hybrid system has been disclosed in Japanese Patent Provisional Publication No. 9-257121. FIG. 5 shows a simplified skeleton diagram of the parallel hybrid system disclosed in the Japanese Patent Provisional Publication No. 9-257121. As shown in FIG. 5, the parallel hybrid system includes an internal combustion engine 112 serving as a primary power source, an electric torque converter 124, and an automatic transmission 118, and also these component parts 112, 124, and 118 are arranged in the longitudinal direction of the vehicle, in that order. The electric torque converter 124 is constructed by an electric motor generator 114 capable of functioning as a generator (generating electricity for example in a regenerative state) as well as an electric motor (driven by electricity for example in a power running state), and a single-pinion planetary-gear system 116 serving as a composition/distribution mechanism capable of mechanically combining two different forces, that is, torque produced by the engine and torque produced by the motor/generator, with each other, and of mechanically distributing the torque produced by the engine into the motor/generator and an input shaft of the automatic transmission 118. The driving force (driving torque) transmitted to the input shaft of the automatic transmission 118 is transmitted through a transmission output shaft 119 via a propeller shaft (not shown) and a differential (not shown) to drive wheels (not shown). As discussed above, in the parallel hybrid system shown in FIG. 5, a usual hydraulic torque converter is replaced with the electric torque converter 124 constructed by the motor generator 114 and the planetary-gear system 116. From the viewpoint of improved fuel economy, it is desirable to use the electric torque converter instead of the hydraulic torque converter, because of relatively great energy loss in the hydraulic torque converter. Torque multiplication action needed for the torque converter can be attained by a torque assist with the electric motor/generator 114 and also by the planetary-gear system 116.
However, if a hybrid vehicle with an automatic transmission using an electric torque converter as discussed previously is largely different from usual automotive vehicles in basic design, an immense expenditure of money may be necessary for investment in plant and equipment. It is undesirable from the viewpoint of productivity and marketability. For the reasons set forth above, it is desirable to provide a hybrid unit which can be installed without adding a large change of design to popular automotive vehicles. Therefore, it is preferable to be able to install or arrange an electric torque converter having a substantially same axial dimension as compared to a hydraulic torque converter within the same installation space of the hydraulic torque converter. This is because, generally, a position of an engine crankshaft end, a position of a transmission input shaft end, and a position of a transmission output shaft end are determined depending upon vehicle requirements, that is, the type and dimensions of automotive vehicle. For this reason, an axial length of the engine crankshaft, an axial length of the transmission input shaft and/or an axial length of the transmission output shaft must be shortened, as a design axial length of the electric torque converter increases. Undesirably, the increased design axial length of the electric torque converter requires a large change in basic design of engine and/or transmission. Also, in the hybrid unit employing both an electric motor/generator and a gear mechanism, a dry chamber in which the motor/generator is installed in a fluid-tight fashion and an oil chamber in which the gear mechanism is provided to insure good gear elements operation. As a matter of course, the dry chamber and the oil chamber must be completely separated from each other. As can be seen from the skeleton diagram of the conventional parallel hybrid system shown in FIG. 5, if a partition wall is simply provided between the composition/distribution mechanism (e.g., the single-pinion planetary-gear mechanism 116) and the motor generator 114 in order to divide an internal space of the electric torque converter into the dry chamber and the oil chamber, there is a problem that the design axial length of the electric torque converter becomes longer than that of the hydraulic torque converter (see the layout of the motor generator 114 and the planetary-gear system 116 in the electric torque converter 124 of FIG. 5 or see the layout of a motor generator 5 and a composition/distribution mechanism 6 shown in FIG. 3A).
Accordingly, it is an object of the invention to provide an electric torque converter mounted on a parallel hybrid vehicle, which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an electric torque converter easily applicable to an automotive vehicle, retaining the same axial dimension as a usual hydraulic torque converter.
In order to accomplish the aforementioned and other objects of the present invention, an electric torque converter mounted on a parallel hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor for propulsion, the electric torque converter comprises an electric motor generator, and a composition-and-distribution mechanism adapted to be located between the engine and a transmission for mechanically combining torque produced by the engine and torque produced by the motor generator with each other and for mechanically distributing the torque produced by the engine into the motor generator and a transmission input shaft of the transmission. A converter case of the electric torque converter comprises a first casing member partitioning the transmission from the electric torque converter, a second casing member located between the engine and the transmission for partitioning the electric torque converter from the exterior, and a third casing member partitioning the motor generator from the composition-and-distribution mechanism and having a large-diameter portion fixedly connected to the first casing member, a medium-diameter portion housing therein the composition-and-distribution mechanism and placing therearound a motor generator rotor of the motor generator so that at least a part of the motor generator rotor overlaps with the composition-and-distribution mechanism in a radial direction, and a small-diameter portion whose inner periphery rotatably supports a rotating shaft arranged coaxially with the transmission input shaft. It is preferable that the electric torque converter may further comprise a one-way clutch located on an inner periphery of the large-diameter portion of the third casing member for inhibiting the transmission input shaft from rotating backward. More preferably, the electric torque converter may further comprise a revolution sensor located between the outer periphery of the third casing member and the inner periphery of the motor generator rotor for sensing a rotor angle of the motor generator rotor.